The replacement drive belt (#26) is too short to slide over the drive gears. It is beyond any reasonable amount coaxing or stretching with something to get it to pop on. What needs to be removed for this belt to be put in place within reason?

I found that if you apply a little finger pressure against the belt as it lines up with the drive gears and rotate the barrel or armature or anything to cause the drive gears to turn, the belt will thread on. You might have to rotate back and forth a bit to get the belt lined up on both gears.

I am now trying to get brush assembly for my 371, Type 1, because I see sparks under the brushes and the sander is running slowly and on the hot side. I hope it is not the armature.

I noticed this sander was slipping sporadically. I disassembled and determine the jack shaft gear was loose on the shaft. I tighten the appropriate nut and it looks like it should be back in business.
My question is:
I removed the gear oil. Which got contaminated with sawdust. What is the appropriate gear oil for the worm drive gear box??